In this case study the electroencephalographic (EEG) activity of a 23 years old snake phobic patient was recorded one week before treatment, one week after successful one-session exposure therapy, and one year later. EEG recordings were obtained at rest and during exposure to pictures of snakes, pictures of equivalent arousing power, and emotionally neutral images, all of them taken from the International Affective Pictures System. Measures of brain dynamics were sample entropy (SampEn) for each EEG signal/channel and phase synchronization between pairs of EEG channels. Results showed dramatic changes in both measures one week after treatment: SampEn increased and phase synchrony decreased at all sites and pairs of channels respectively. At follow-up, however, we found patterns of entropy and synchrony change across conditions that were similar to the pre-treatment ones, while the patient did not report any fear at all. Despite the limitations of single case studies, these results suggest that the exposure-induced changes in EEG entropy and synchronization are large but transient. The transient increase of the brain’s flexibility could be one of the working neurophysiological mechanisms of exposure therapy.

In the present study a computer-assisted exposure-based treatment was applied to 54 flight phobics and the predictive role of vagally mediated heart rate (HR) variability (high frequency, 0.15-0.4 Hz band power) and heart rate entropy (HR time series sample entropy) on treatment outcome was investigated. Both physiological measures were taken under controlled breathing at 0.2 Hz and during exposure to a fearful sequence of audiovisual stimuli. Hierarchical regression analyses were conducted to assess the predictive power of these variables in these conditions on treatment self-report measures at the end of treatment and at 6 months follow-up, as well as on the behavioral treatment outcome (i.e. flying at the end of treatment). Regression models predicting significant amounts of outcome variance could be built only when HR entropy was added to the HR variability measure in a second step of the regression analyses. HR variability alone was not found to be a good predictor of neither self-reported nor behavioral treatment outcomes.

Research within the framework of the nonlinear dynamical systems (NDS) in the field of anxiety disorders has shown that greater irregularity/complexity appears in the output from healthy systems. In this study we measured the Heart rate variability (HRV) and the sample sntropy (SampEn) of the ECG mV time series of fearful flyers (N = 15) and a matched control group (N = 15) when confronted with three combinations of feared stimuli (pictures, sounds, and pictures with sounds) as well as relaxing stimuli (pictures and sounds). Fearful flyers had lower SampEn than controls in all conditions, including baseline. Non-phobics showed significant entropy decreases from baseline in two out of three exposure conditions. No differences on HRV were found between groups, and HRV was not sensitive to condition changes. The main finding of the study is that the SampEn calculated on very short ECG mV recordings (10 to 60 seconds, easy to obtain in clinical settings) may be a useful diagnostic measure since it can distinguish fearful from non-fearful flyers.